1. Field of the Invention
The invention relates to a method for operating a powertrain having at least one drive unit and an automatic transmission.
2. Description of the Related Art
Automatic transmissions constructed as change transmissions having a multi-stage main transmission and a range-change gearbox located upstream or downstream of the main transmission as well as a splitter gearbox located upstream or downstream of the main transmission, have been known for some time and are preferable for use in commercial vehicles. By means of, for example, a two-stage type splitter gearbox with a gear ratio step corresponding to approximately half of a medium gear ratio step between two consecutive gear ratio stages of the main transmission, the gear ratio steps of the main transmission are halved and the total number of available gears of the change transmission is doubled. By means, for example, of a two-stage range-change gearbox having gear ratio step lying approximately at a medium gear ratio step between two consecutive gear ratio stages of the main transmission over the entire gear ratio step of the main transmission the transmission ratio spread of the change transmission is basically doubled and the total number of gears available is again doubled.
Automatic transmissions are also known that consist of only a main transmission. The splitter gearbox and the range-change gearbox are thereby optional components of an automatic transmission, whereby the main transmission of a range-change gearbox may be either upstream or downstream and/or a splitter gearbox may be upstream or downstream. Automatic transmissions having interlocking gearshift elements are to be distinguished from automatic powershift transmissions with friction locking gearshift elements.
Furthermore, it is known that powertrains of this sort in a vehicle having an automatic transmission may comprise an auxiliary drive, whereby an auxiliary drive may be referred to as a Power Take Off (PTO). A distinction is made in auxiliary drives between transmission-side and motor-side auxiliary drives on the one hand and on the other hand between stationary auxiliary drives and mobile auxiliary drives.
A motor-side auxiliary drive branches at a point directly off the drive unit, whereby a transmission-side auxiliary drive branches at a point directly off the transmission. Stationary auxiliary drives may only be operated when the vehicle is stationary, specifically when the automatic transmission is in neutral, i.e. when the power flow, or respectively, when the force flow from the drive unit to the axle drive is interrupted. Mobile auxiliary drives, on the contrary, may be operated when the transmission is engaged, i.e. when the power flow, or respectively, the force flow from the drive unit to the axle drive is not interrupted.
So far, stationary transmission-side auxiliary drives of a powertrain for a vehicle of this sort having an automatic transmission can only be engaged in a stationary vehicle, and thereby be activated. Furthermore, to date, when a transmission-side mobile auxiliary drive is engaged, or respectively, is activated, the execution of gear shifting is impeded such that it is only possible to drive in a single gear when the auxiliary drive is engaged, or respectively, is activated, and therefore within a limited speed range. Therefore it is necessarily the case that, according to the prior art, the engagement, or respectively, activation of a transmission-side, mobile auxiliary drive may only be carried out on a stationary vehicle, at a relatively low gear, specifically a start-up gear, because start-up must be possible from a stationary state.
The present invention relates to a method for operating a powertrain with an automatic transmission and a transmission-side, mobile auxiliary drive with which it is possible to engage, and thereby activate, the transmission-side, mobile auxiliary drive while the vehicle is also in motion.
From the DE 197 08 020 A1, a method is known for operating a powertrain with an automatic or semi-automatic transmission and an auxiliary drive, with which the engagement and thereby activation of an auxiliary drive is only possible when the vehicle is stationary.